ClickHouse/src/Common/ZooKeeper/ZooKeeperLock.h

#pragma once
#include <Common/ZooKeeper/ZooKeeper.h>
#include <Common/ZooKeeper/KeeperException.h>
#include <memory>
#include <string>

namespace Poco { class Logger; }

namespace zkutil
{

/** Caveats: usage of locks in ZooKeeper is incorrect in 99% of cases,
  *  and highlights your poor understanding of distributed systems.
  *
  * It's only correct if all the operations that are performed under lock
  *  are atomically checking that the lock still holds
  *  or if we ensure that these operations will be undone if lock is lost
  *  (due to ZooKeeper session loss) that's very difficult to achieve.
  *
  * It's Ok if every operation that we perform under lock is actually operation in ZooKeeper.
  *
  * In 1% of cases when you can correctly use Lock, the logic is complex enough, so you don't need this class.
  *
  * TLDR: Don't use this code if you are not sure. We only have a few cases of it's usage.
  */
class ZooKeeperLock
{
public:
    /// lock_prefix - path where the ephemeral lock node will be created
    /// lock_name - the name of the ephemeral lock node
    ZooKeeperLock(
        const ZooKeeperPtr & zookeeper_,
        const std::string & lock_prefix_,
        const std::string & lock_name_,
        const std::string & lock_message_ = "",
        bool throw_if_lost_ = true);

    ~ZooKeeperLock();

    void unlock();
    bool tryLock();
    bool isLocked() const;
    const std::string & getLockPath() const;

private:
    zkutil::ZooKeeperPtr zookeeper;

    std::string lock_path;
    std::string lock_message;
    bool throw_if_lost{true};
    LoggerPtr log;
    bool locked = false;

};

std::unique_ptr<ZooKeeperLock> createSimpleZooKeeperLock(
    const ZooKeeperPtr & zookeeper, const String & lock_prefix, const String & lock_name, const String & lock_message, bool throw_if_lost = true);

}